...and this is the same Eminem that reportedly spouts "F--- You Mrs. Cheney" (referring, of course, to the wife of the current VP) in one of his songs. Why?

Because he can.

As one apt pundit at NRO (or was it Washington Times?) noted:

Because we live in an age where words are not ALLOWED to hurt by virtue of a litany of speech codes, invective is no longer reserved for truly startling occassions -- and it consequently no longer has any meaning. Phrases like Eminem's amount to mere "spit-up" at worst.